There is conventionally known a construction machine including an engine and an air cleaner connected to the engine. Air cleaners thus provided in a construction machine are disclosed, for example, in Japanese Utility Model Application Laid-open No. S63-48965. Besides, an air cleaner including an evacuator for discharging dusts and placed on an upper surface of a hood as a house cover which covers an engine room is disclosed in Japanese Patent Application Laid-open No. 2003-184670. Furthermore, Japanese Patent Application Laid-open No. 2003-184670 discloses a technique including: providing an air ejection port in an upper portion of a house cover corresponding to the air-cleaner placement surface 29; directing the air ejection port to the lower side of an evacuator; and ejecting a part of cooling air sucked into the inside of the house cover by a cooling fan during engine operation to blow off the dusts. This technique, however, requires a complicated structure which increases cost and involves various problems such as leakage of engine noise or generation of ejection sound. Furthermore, the cooling air cannot be ejected until the pressure inside the house cover has been sufficiently increased, which hinders the function of blowing off dusts from being effective. On contrary, when the function of blowing off dusts is effective, the dusts may be widely diffused to thus give a negative effect on equipment.